Fix broken links in unetr_btcv_segmentation_3d.ipynb (#1828)

Fixes #1827

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

Signed-off-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>

Author: KumoLiu

3d_segmentation/unetr_btcv_segmentation_3d.ipynb

@@ -19,7 +19,6 @@
     "\n",
     "\n",
     "This tutorial demonstrates how to construct a training workflow of UNETR [1] on multi-organ segmentation task using the BTCV challenge dataset.\n",
-    "![image](https://lh3.googleusercontent.com/pw/AM-JKLU2eTW17rYtCmiZP3WWC-U1HCPOHwLe6pxOfJXwv2W-00aHfsNy7jeGV1dwUq0PXFOtkqasQ2Vyhcu6xkKsPzy3wx7O6yGOTJ7ZzA01S6LSh8szbjNLfpbuGgMe6ClpiS61KGvqu71xXFnNcyvJNFjN=w1448-h496-no?authuser=0)\n",
     "\n",
     "And it contains the following features:\n",
     "1. Transforms for dictionary format data.\n",
@@ -51,7 +50,7 @@
     "3. [Efficient multi-atlas abdominal segmentation on clinically acquired CT with SIMPLE context learning (MIA)](https://www.sciencedirect.com/science/article/abs/pii/S1361841515000766?via%3Dihub)\n",
     "\n",
     "\n",
-    "![image](https://lh3.googleusercontent.com/pw/AM-JKLX0svvlMdcrchGAgiWWNkg40lgXYjSHsAAuRc5Frakmz2pWzSzf87JQCRgYpqFR0qAjJWPzMQLc_mmvzNjfF9QWl_1OHZ8j4c9qrbR6zQaDJWaCLArRFh0uPvk97qAa11HtYbD6HpJ-wwTCUsaPcYvM=w1724-h522-no?authuser=0)\n",
+    "![image](../figures/BTCV_organs.png)\n",
     "\n",
     "\n",
     "\n",